Experimental design. Briefly, animals were sensitized by intradermal injection of a suspension of 3, 1, and 0.1 mg of TMA in 0.1 ml corn oil on day 1, 10 and 20, respectively. In double sensitization experiments, animals were sensitized as above but also administered 0.3 mg ovalbumin in 0.1 ml PBS by intradermal injection. Animals were exposed to an aerosol of PBS or TMA conjugated to guinea pig serum albumin (TMA-GPSA) on day 30 to 34. One group of animals was exposed to PBS on day 30-33 followed by a high dose TMA-GPSA (0.15%) exposure once for 15 min on day 34. One group of animals was exposed to a low dose TMA-GPSA (0.03%) for 15 min each day on 5 consecutive days. ACh responsiveness was evaluated 24 hours after the last exposure. The early airway response to TMA-GPSA was measured one hour after the completion of the ACh responsiveness (some changes were made on day 35 for other experiments, see study design/protocol section). Bronchial alveolar lavage (BAL) fluid was taken immediately after the assessment of early airway response.